1. Technical Field
The present invention relates to a shape memory alloy actuator.
2. Description of Related Art
Shape memory alloy actuators which include a shape memory alloy have hitherto been used.
In a shape memory alloy, there are two states namely, an austenitic phase and a martensitic phase, and when a temperature is low, the state changes to the martensitic phase, and when the temperature is high, the state changes to the austenitic phase. Moreover, particularly at the time of transition (a reverse transformation) from the martensitic phase to the austenitic phase, a large distortion-restoring force is generated due to a small temperature difference. An actuator in which, a shape change of this shape memory alloy is used has superior characteristics from a view point of small-sizing and making light the weight of the actuator.
For instance, in Patent Document 1, a conventional shape memory alloy actuator has been described.
FIG. 3 is a partial cross-sectional front view of a conventional shape memory alloy actuator 101. The shape memory alloy actuator 101 has an arrangement in which, one end of a wire material of a shape memory alloy 12 is let to be a fixed end 12a, and the other end of the shape memory alloy 12 is let to be a movable end 12b, and the movable end 12b is driven by a stress due to a bias spring 21 and a contraction force which is generated when a length of the wire material of the shape memory alloy 12 has changed by a change in temperature due to heating by applying an electric current to the wire material of the shape memory alloy 12. Moreover, saving of space of the shape memory alloy actuator 101 has been made possible by covering the wire material of the shape memory alloy toward the fixed end 12a, by a tube member 11 which has an insulating property and which can be bent.
In the shape memory alloy actuator 101, an amount of distortion is controlled by the change in temperature of the shape memory alloy 12 due to heating by applying an electric current. As a method for controlling, a method of controlling an amount of heating by applying an electric current by feeding back a resistance value of the shape memory alloy 12 is available.